Microwave signals are extremely high frequency (HF) signals, usually in the gigahertz range. They are used to transmit large amounts of video, audio, RF, telephone, and computer data over long distances. They are used in commercial and military applications, including communications to satellites, airplanes and the like. Frequencies are divided into various bands such as the S-band (2-3.5 GHz), Ku-band (10.7-18 GHz), Ka-band (18-31 GHz), and others such as the X-band etc.
Polarization is a characteristic of the electromagnetic wave. Four types of polarization are used in satellite and other transmissions: horizontal; vertical; right-hand circular (RHCP); and left-hand circular (LHCP). Horizontal and vertical polarizations are types of linear polarizations. Linear and circular polarizations are well known in the art. A wave is made up of an electric field ‘E’ and a magnetic field ‘M’. When a wave of wavelength ‘λ’ is transmitted into free space from an antenna, the orientation of its electric field E with respect to the plane of the earth's surface determines the polarization of the wave. If the wave is oriented such that the E field is perpendicular to the earth, the wave is referred to as vertically polarized. If the ‘E’ field is parallel to the earth's surface, the wave is horizontally polarized.
FIG. 1A (prior art) is a solid rear left side perspective view of the assembly of the multi-frequency waveguide internal structure 210, an embodiment of the closest prior art from U.S. Pat. No. 7,408,427 which is incorporated herein by reference in its entirety. It has two separate frequency sections. A simplified block diagram of multi-frequency waveguide internal structure 210 is found in FIG. 1B. Multi-frequency waveguide internal structure 210 will is shown in FIG. 3A in a three sectional split block configuration. It can be seen how the prior art invention provides a compact internal structure as a waveguide feed to transmit and/or receive microwave signals. The path will be described as receiving signals into horn input/output area 207 and exiting to receiver electronics within one of the four ports described herein. Multi-frequency internal structure 210 comprises horn input/output area 207, where an input signal is received or an output signal is transmitted. An input signal passes into first common junction 208, and into LF filters 212 as polarized. The lowest frequency signal then moves through LF 90° polarizer 214. LF 90° polarizer 214 allows a 90° phase shift that is necessary for circularly polarized signals. Magic tee (hybrid tee) section 216 recombines the two orthogonal components for the lowest frequency signal. Magic tee (hybrid tee) 216 is a four port, 180 degree hybrid splitter, realized in a waveguide. The signal then goes to receiver electronics through LF RHCP port 301 or LF LHCP port 204. For linear polarization, polarizer 214 and magic tee (hybrid tee) 216 are not needed. In this case, vertical and horizontal polarization ports would be placed directly after each LF filter 212, extended to the sidewall of the split block. Dummy ports 213 are connected to common junction 208 when a symmetrical structure is needed to eliminate unwanted modes and to help axial ratio. Junction 224 moves higher frequency signals to HF filtering section 228, and then to HF 90° polarizer 222. Dummy ports 218 are also connected to the junction and are required when a symmetrical structure is needed to eliminate unwanted modes and to help axial ratio. The two orthogonal components of the HF signal are recombined by magic tee (hybrid tee) 226 and then exit out through HF RHCP port 302 or HF LHCP port 205. For linear polarization, polarizer 222 and magic tee (hybrid tee) 226 are not needed. In this case, vertical and horizontal polarization ports would be placed directly after HF junction 224, extended to the sidewall of the split block. Multi-frequency waveguide internal structure 210 has axial length L2.
As can be seen on FIG. 1A, the prior art invention provides a compact subassembly without flanges or mounting bolts that add to the complexity of earlier prior art waveguide feeds. This reduces the cost of manufacture and assembly, and also reduces the physical size of the waveguide feed. Multi-frequency waveguide internal structure 210 can easily be sectioned in a three split block configuration for ease of manufacture, which is described below. It should be noted that a dual band four-port waveguide feed is described but this layout can easily be expanded to accommodate additional frequency bands and associated waveguide ports.
FIGS. 2A, 2B show the left side frontal perspective views of the an embodiment of the present invention, which is a split block, three section compact assembly comprising all of the functions as previously described in FIG. 1A above. Compact multi-frequency feed 200 is shown with a layout in a three split block structural configuration. Split block sections include center block 202, which is between frontal block 203 and rear block 201. Shown are horn input/output area 207, LF LHCP port 204 and HF LHCP port 205. FIG. 5B is the identical perspective view as shown in FIG. 5A and additionally shows multi-frequency waveguide internal structure 210 (ref. FIG. 1A).
From FIGS. 2A and 2B it can be seen that the blocks are split about the zero current line for each of the waveguide structures in order to prevent degradation in electrical performance. The prior art as well as the present invention could also comprise multiple central blocks as necessary to obtain the desired number of frequency bands for the waveguide feed.
FIG. 3A is an enlarged right side frontal perspective view of the compact multi-frequency feed 200 and its three blocks; center block 202, frontal block 203, and rear block 201 of an embodiment of the prior invention. Also shown is LF LHCP port 204 and horn input junction 207. Inner sections will be described below in FIGS. 4A, 4B.
FIGS. 4A, 4B show the front and the rear views of the center block 202 of the compact multi-frequency feed 200. The front face of center block 202 (FIG. 4A) will be attached to the rear face of frontal block 203 and the rear face of center block 202 will be attached to the front face of rear block 201.
FIG. 4A shows HF filtering section 228 that allows only higher frequency signals to propagate to HF junction 224. Shown are LF LHCP port 204B, LF magic tee (hybrid tee) 216B, LF polarizers 214B, first common junction 208B, LF low pass filters 212B, and dummy ports 2138.
FIG. 4B is a detailed view of the rear of center block 202 with the internal recesses made into the material. HF junction 224A is connected to waveguide polarizer 222A. Waveguide polarizer 222A can be any device that creates a 90° phase delay between the two liner signals traveling in the two orthogonal paths. If the signal is linearly polarized the vertical and horizontal polarization ports would be placed directly after the HF junction 224A, and then extended to the sidewall of the split block. In this layer like the last, dummy port sections 218A are required when a symmetrical structure is required to eliminate unwanted modes and to help axial ratio. The RHCP signal from the lower frequency band travels through LF RHCP port 301A to its final destination in LF RHCP port 301. Shown is HF LHCP port 205A and hybrid tee 226A.
What is needed in the art is a feed network with close to the prior art efficiencies, but with a higher density packaging capability.
The present invention in various embodiments provides an efficient layout of waveguide components, compared to prior art, for multi-frequency band antenna feeds. It uses folded (also called curved or bent) elements to greatly reduce the center point distance in array packaging embodiments. It allows for compaction of components, maintains good electrical performance, is mechanically robust, eliminates flange connections between components, and is very cost effective to produce in small or large quantities. It can be applied to waveguide components with circular, rectangular, square, elliptical, co-axial, or any cross sections that can be created by making recesses in the split block.
The present invention allows waveguide components that can be machined in a split block configuration. Recesses are created in two pieces of material to produce the waveguide components. The components are formed after assembly of each respective split block. It eliminates the need for flanges between different components. Assembly of the blocks can be done by any method that can effectively hold the blocks together such as bolts, brazing, soldering, and adhesive bonding. Various layouts can be realized using any number of fabrication methods, such as brazing, electroforming, and machining. The apparatus and method of the present invention would reduce size by a factor of about two or more, especially in the dimension of width compared to FIG. 4A length. For example, a multi-frequency waveguide in the range of the Ka-band (18-31 GHz), would typically be about 4″ depth×4.5″ width by 8″ long in prior art, whereas it has been demonstrated that the present invention, in the same frequency range, would reduce the size to about one inch in diameter. Typical split block sections are in a range of about 2″ by 2.5″ with a depth of about 0.4″ to about 1.2″. The significant reduction in axial length is a major advantage of the prior art invention shown in FIGS. 1-4B, especially in packaging waveguides in small compartments aboard satellites, aircraft etc. The reduction in diameter size in the present invention by folding central elements and eliminating dummy ports provides enormous advances in high density array packaging. This process is very cost effective and significantly reduces the size of multi-frequency band antenna feeds. The present invention can be applied to waveguide components with circular, rectangular, square, elliptical, co-axial, or any cross sections that can be created by making recesses in the split block. Split block fabrication techniques allow very cost effective manufacturing both during fabrication and assembly regardless of quantities involved.
Split block manufacturing and assembly is used to create the unique structures used in multi-frequency band antenna feeds. For a dual frequency band feed only three blocks are required. A tri-band feed requires an assembly of four blocks. This technique can be used for as many unique frequency bands as are desired by the application for which they are intended for use.
Elimination of the need for flanges in the prior art between the different components required by the feed eliminates the risk of electrical performance degradation due to flange misalignments and imperfections.
Created blocks are joined at the zero current line of the components, which practically eliminates electrical performance degradation that may arise due to misalignment between two adjacent blocks. There is no limit to the frequency bands that can be applied to it as long as a practical method of fabrication is available. The layout provides the ability to use standard tracking systems.